1. Field of the Invention
The present invention relates to a manufacturing method of epitaxial silicon wafer(s) and a substrate cleaning apparatus.
2. Description of Related Art
Epitaxial silicon wafers have been conventionally known to have: substrates made of silicon monocrystal; and epitaxial layers formed on surfaces of the substrates.
Since contamination of an epitaxial layer of such an epitaxial silicon wafer with metal impurities may deteriorate device properties, such contamination of the epitaxial layer with metal impurities is eliminated by gettering.
An exemplary method of enhancing gettering capability is to form oxygen precipitation nucleation within a bulk by adding nitrogen to a crystal during pulling-up, trap metal impurities within the oxygen precipitation nucleation, and eliminate the metal impurities.
On a surface of such a nitrogen-doped substrate, COP (crystal originated particle), one of micro defects, is present. An inner wall of the COP is known to be covered with oxide film nitride film.
It has been found that, when an epitaxial layer is further formed on the substrate surface in this state, the oxide film nitride film of the inner wall of the COP causes stacking faults (hereinafter may be abbreviated as SF), which may lead to a defect on a surface of an epitaxial wafer.
In view of such a problem, according to a known technique, a substrate is soaked into a solution of fluorinated acid or a substrate surface is cleaned with a solution of fluorinated acid before an epitaxial layer is formed (see, for instance, Document 1: JP-A-2002-20200).
According to another known technique, a substrate is pre-annealed before an epitaxial layer is formed (see, for instance, Document 2: JP-A-2003-73191).
However, the cleaning of the substrate with the solution of fluorinated acid as disclosed in Document 1 cannot sufficiently eliminate the oxide film.nitride film of the inner wall of the COP, and requires a longer time for cleaning.
In addition, unless precious metal ion within the cleaning solution of fluorinated acid is sufficiently blocked, a difference in electric charge between the precious metal ion and the silicon may cause a defect on the surface.
On the other hand, although the pre-annealing of the substrate before the formation of the epitaxial layer as disclosed in Document 2 is effective to a certain degree, precipitate formed on the surface by heat treating may cause a defect on the surface again.